From 5206e9ca22864d33f2e971c35297cbfc5fb58a4a Mon Sep 17 00:00:00 2001
From: lbenedar <lbenedar@local.lab>
Date: Tue, 17 Mar 2026 12:44:59 +0300
Subject: [PATCH] ch4.3\

---
 cmd/api/helpers.go | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/cmd/api/helpers.go b/cmd/api/helpers.go
index 29b5785..4848e90 100644
--- a/cmd/api/helpers.go
+++ b/cmd/api/helpers.go
@@ -7,6 +7,7 @@ import (
 	"io"
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/julienschmidt/httprouter"
 )
@@ -41,11 +42,17 @@ func (app *application) writeJSON(w http.ResponseWriter, status int, data envelo
 }
 
 func (app *application) readJSON(w http.ResponseWriter, r *http.Request, dst any) error {
-	err := json.NewDecoder(r.Body).Decode(dst)
+	maxBytes := 1_048_576
+	r.Body = http.MaxBytesReader(w, r.Body, int64(maxBytes))
+	dec := json.NewDecoder(r.Body)
+	dec.DisallowUnknownFields()
+
+	err := dec.Decode(dst)
 	if err != nil {
 		var syntaxError *json.SyntaxError
 		var unmarshalTypeError *json.UnmarshalTypeError
 		var invalidMarshallError *json.InvalidUnmarshalError
+		var maxBytesError *http.MaxBytesError
 
 		switch {
 		case errors.As(err, &syntaxError):
@@ -59,11 +66,20 @@ func (app *application) readJSON(w http.ResponseWriter, r *http.Request, dst any
 			return fmt.Errorf("body contains incorrect JSON type for field (at character %d)", unmarshalTypeError.Offset)
 		case errors.Is(err, io.EOF):
 			return errors.New("body must be not empty")
+		case strings.HasPrefix(err.Error(), "json: unknown field"):
+			fieldName := strings.TrimPrefix(err.Error(), "json: unknown field")
+			return fmt.Errorf("body contains unknown key %s", fieldName)
+		case errors.As(err, &maxBytesError):
+			return fmt.Errorf("body must not be larger than %d bytes", maxBytesError.Limit)
 		case errors.As(err, &invalidMarshallError):
 			panic(err)
 		default:
 			return err
 		}
 	}
+	err = dec.Decode(&struct{}{})
+	if err != io.EOF {
+		return errors.New("body must only contain a single JSON value")
+	}
 	return nil
 }